1. Field of the Invention
The present invention relates to a video tape recording apparatus and more particularly to a rotary magnetic head type recording apparatus to be applied to a commercially-available high definition video tape recorder, for example.
2. Description of the Prior Art
In a commercially-available high definition video tape recorder (hereinafter simply referred to as a VTR), for example, both a video signal and a PCM (pulse code modulated) audio signal are recorded on a magnetic tape by using a rotary magnetic head, wherein the audio signal is composed of two systems each of which includes two channels of audio signals, that is, four channels of audio signals in total.
It has been proposed to enable in a VTR an operation such as a high-speed program search in a reproducing mode by providing an index signal which is recorded and reproduced by a rotary magnetic head. In this case, it has been proposed to provide a recording area for the index signal at a non-effective picture portion of the video signal or at a data portion for the PCM audio signal. However, if the recording area of the index signal is provided at these areas, the index signal cannot be erased or rewritten and also a new index signal cannot be added, thereby strictly limiting the flexibility of the index signal.
On the other hand, in VTRs where recording areas of the video signal and the audio signal are separately provided, it has been proposed to record the index signal by using an area between the recording areas of the video and audio signals, that is, a guard band area. Namely, if the video signal and the two systems of audio signals as described above are recorded, a recording pattern thereof on a tape T will be such as shown in FIG. 1. As shown in FIG. 1, a guard band area with a predetermined length with respect to the scanning direction of the head is provided in each of areas between the recording area of the video signal and the recording area of the audio signal and also between the recording areas of the two systems of audio signals, and it has been proposed to record an index signal by using these guard band areas.
However, in this case, the following problems arise.
Namely, signals forming respective recording areas on a track are generally formed with reference to a signal generated from a pulse generator (PG) or a frequency generator (FG) provided on a rotary head drum, so that a timing deviation when the signals are formed may cause a recording deviation from a position on a tape where the signals should be recorded. The reasons for the deviation include an adjustment error of a rotary head type recording and/or reproducing apparatus, change of a timing signal due to aging of an apparatus, change of a tape running state due to changes in relationships between a tape and an apparatus caused by aging, or differences in running states among compatible apparatus, etc. Thus, this recording deviation is recognized as a tolerance in a tape format.
Accordingly, positions of respective recording areas on a tape vary within a tolerance due to aging changes, etc., so that there is a possibility that the length of a guard band area may decrease due to an operation of after-recording and so on.
Namely, suppose that a recording pattern of video and audio signals recorded by a first apparatus deviates by +aH as shown in FIG. 2A, where .+-.aH represents the above described tolerance and H represents the horizontal synchronizing period, while a recording pattern of a first audio signal recorded by an after-recording operation using a second apparatus deviates by -aH as shown in FIG. 2B. Then, the recording pattern of the video and both audio signals is as shown in FIG. 2C, wherein a length of the remaining guard band area is only (b-2a)H, where bH represents the reference length of the guard band area.
Further, in case of subsequent recording of an index signal in the guard band area, an additional tolerance due to the recording of the index signal must be taken into consideration, so that a length of the guard band area where the index signal can be recorded will be only (b-4a)H.
If a length necessary for recording the index signal is lH, then the length of the guard band area is required to be (bH=(l+4a)H in view of the above described tolerances, where bH represents the reference length of the guard band area. However, if a guard band area with this long length is provided as the reference guard band area, then the recording areas of the audio and video signals must be shortened disadvantageously.